The gluten-free, casein-free (GFCF) diet is widely used by families of children with autism spectrum disorders (ASD). Despite its popularity, there is limited evidence in support of the diet. The purpose of this article was to identify and evaluate well-controlled studies of the GFCF diet that have been implemented with children with ASD. A review of the literature from 1999 to 2012 identified five studies meeting inclusion criteria. Research rigor was examined using an evaluative rubric and ranged from "Adequate to Strong." In three of the studies, no positive effects of the diet were reported on behavior or development, even after double-blind gluten and casein trials. Two studies found positive effects after 1 year but had research quality concerns. Reasons why families continue to expend effort on GFCF diets despite limited empirical evidence are discussed. Recommendations are that families should invest time and resources in more robustly supported interventions and limit GFCF diets to children diagnosed with celiac disease or food allergies.